1. Field of the Invention
Apparatuses and methods consistent with the present invention are generally related to storage tanks and are specifically related to storage tank filling systems which prevent overflow during and subsequent to filling and to storage tank venting systems for venting a storage tank to the atmosphere efficiently and environmentally.
2. Description of the Related Art
It is well known to use storage tanks for holding a variety of fluids such as oil, gasoline, and diesel fuel to name a few. Proper filling of storage tanks is a universal concern, as overfilling of storage tanks may result in spillage, damage to the tank or filling equipment, contamination of land or ground water, or other serious and potentially dangerous results. Concerns over spillage of the tank contents are particularly acute when the tank contents are flammable, toxic and/or environmentally hazardous.
Spillage from fuel tanks on pleasure boats and other marine vessels is particularly troublesome. Some contemporary estimates of such fuel spillage are in excess of six million gallons annually in the United States alone. Globally, fuel spillage is many times this amount. The resultant fuel losses are economically and ecologically detrimental in terms of wasted fuel resources and environmental contamination.
An internal fuel tank on a marine vessel is typically provided with a vent to enable vapor and fumes to escape under pressure while fuel is being pumped into the fuel tank via the fuel fill tube. As the engine consumes fuel, air is drawn into the tank via the air vent to fill the space from the consumed fuel. Venting is also necessary to accommodate expansion of the fuel when it is heated. Conventionally, during filling of the fuel tank, some fuel may be discharged through the vent into the water as the attendant attempts to fill the tank to capacity. In fact, it is not unknown for filling attendants to purposely fill the tank until fuel is discharged from the vent, using this as an indication that the tank is completely full. It is also possible that fuel may be discharged through the vent subsequent to filling. For example, fuel can be discharged through the vent in a tank filled to capacity as a result of the boat listing from side to side due to waves, wind or other causes. Also conventionally, fuel may be discharged through the vent in a tank filled to capacity if a subsequent rise in ambient temperature causes the fuel to expand.
The use of fuel dispensing nozzles that automatically shut off the flow of fuel to the tank when the tank is full have been used to avoid fuel spillage during filling. These nozzles typically operate by sensing a pressure change at an end of the nozzle that results from fuel backing up within the tank fill tube. Use of a fuel dispensing nozzle with automatic shut-off will prevent fuel discharge through the fill tube during filling if the fill tube is properly designed to trigger the shut-off at the appropriate time. However, with many designs the automatic shut-off may be triggered only to have fuel surge out of the vent or out of the tank fill tube because of pressure trapped in the tank. Because of the location of the vent in many applications, it is also possible that fuel will be discharged through the vent during filling. Discharge through the vent may also occur after filling, even if the automatic shut-off is triggered. For example, if the tank is filled to near capacity, fuel can be discharged through the vent due to boat listing or fuel expansion.
A conventional nozzle 10 is illustrated in FIG. 1. Fuel is pressurized in the nozzle passage 1 by a pump (not shown). The flow of fuel is blocked in the nozzle 10 by a valve 3 that is held in a closed position by a spring 2. The valve 3 is connected to a hand-operated trigger 4 at a pivot point 5. The trigger 4 is also connected to a piston 6 at a second pivot point 7. The piston 6 is locked in a dispensing position by a pin 8 that forces balls 9 into a groove in the nozzle housing 11. The pin 8 is connected to a diaphragm 12 that is held in position by a second spring 13. When fuel is dispensed, the trigger 4 is lifted, lifting the pivot point 5 and the valve 3, allowing fuel to flow. The fuel travels to a venturi 15 where a spring loaded ball and seat create a vacuum in the passage 16 that is in communication with the diaphragm 12. The passage 16 is also open to atmospheric pressure through a hole 17 near the end of the dispensing nozzle. When fuel is being dispensed, the pressure in the passage 16 is lowered by the venturi 15, but is replaced by atmospheric pressure through the hole 17 in the nozzle. During conventional automatic shut-off, when the hole 17 is covered by fuel surging up from the tank's fill tube, the pressure drops in the passage 16, drawing the diaphragm 12 against the second spring 13, and the pin 8 is lifted from its locking position. Thus, the piston 6 moves to release the pivot point 7 in the trigger. When the pivot point 7 is moved, the trigger 4 is ineffective and the spring 2 pushes the valve 3 into the closed position, stopping the flow of fuel.
Some prior approaches to preventing spillage rely on the use of a reservoir designed to capture overflow. However, these approaches require additional parts and the use of a reservoir takes up more space on the vessel. None of these approaches addresses the above-mentioned drawbacks of relying on the automatic shut-off feature of existing fuel dispensing nozzles.
Accordingly, there is a need for a system and method that prevents spillage both during and after filling of a storage tank. It would be desirable to have such a system and method of overflow prevention that facilitates use of automatic shut-off nozzles and does not require provision of an overflow reservoir.